The present invention concerns cable connectors for joining individual lengths of cable intended for use in hostile environments, and more particularly concerns connectors customarily used to join lengths of tensioned electromechanical cable utilized in downhole petroleum drilling and logging operations. Such cable generally comprises an inner flexible conductor wire which is surrounded by an insulating material which in turn is surrounded by an outer covering of strong braided steel wires. The braided steel wires are generally referred to as the cable's armor. It is this covering which provides the cable with excellent tensile strength characteristics.
The cable connector of the present invention is able to reliably withstand extreme temperature and pressure environments, as well as high tensile loads. The cable connector may be employed within an active drill string to connect lengths of cable utilized for transmitting data from downhole sensing equipment to surface receiving equipment in measurement while drilling operations or in well logging operations. Measurement while drilling is commonly referred to as MWD.
In well drilling operations, it is sometimes desirable to obtain information about conditions existing in and around the drill bit. MWD sensing equipment is deployed for this purpose in the drill string near the drill bit. One method of transmitting the data from this downhole sensing equipment to the surface receiving equipment is through pressure pulses in the drilling mud. Mud pulse telemetry, though generally reliable, suffers from low data transmission rates. Another method of relaying the data is via electric current flowing through cable which links the downhole sensing equipment with the surface receiving equipment. This method is capable of achieving high data transmission rates, but suffers from reliability problems. One of the most frequent causes of reliability problems is the failure of the cable connectors which are used to link multiple sections of the cable together into one continuous data link which connects the downhole sensing equipment to the surface receiving equipment. Multiple sections of cable are generally required because the cable string has to be lengthened by adding such sections as drilling progresses. This can result in many cable connectors being deployed in the hostile environment existing within the drill string. The failure of any one cable connector is generally sufficient to breach the data link.
Most prior art cable connectors are unsuitable for use in hostile environments, such as active drill strings transmitting pressurized fluids to drill bits. The cable connector described in U.S. Pat. No. 3,694,793, for example, is considered unacceptable in such an environment since the cable connector would not adequately seal the electrical conductors from the drilling fluids. In addition, such a cable connector may inadvertently come apart when downhole fluid pressure acts upon the latch-type coupling designed to release when the tabs are pressed together.
U.S. Pat. No. 4,375,310 discloses a cable connector for interconnecting lengths of armored cable used in MWD operations. The cable connector comprises an electrical contact securely mounted within each of a pair of housings, so that the electrical connection is simultaneously made with the mechanical connection as the housings are coupled together. Problems are encountered when employing this latter connector. Cable tension is transmitted to the electrical connection, and this can cause the electrical connection to separate. Also, although this cable connector seeks to provide an improved housing for sealing an internal electrical connection chamber from the external conductive drilling fluids, the protection provided by such a housing ends to deteriorate due to high temperatures, high pressures, debris on elastomeric sealing surfaces and repeated use. Each cable connector includes many components, which decreases reliability and increases the cost of manufacture. When considering the reliability and expense of such cable connectors, one must recognize that a large number of cable connectors may be required in an MWD operation and that extreme downtime expenses can be incurred to first detect and then subsequently correct a particular defective cable connector.
Cable sections are frequently cut to the desired length at the drill site and cable connectors are attached to the cable sections. A good deal of time is necessary to properly assemble and disassemble prior art cable connectors, and accordingly, expensive drilling operations may be slowed by using such cable connectors. In addition, prior art cable connectors are difficult to repair in field operations, partly because of the number and precision of the components. Finally, prior art cable connectors cannot be easily and quickly cleaned, and the electrical connection cannot be easily inspected by the operator.
The present invention overcomes the disadvantages of prior art cable connectors, and the apparatus described herein should improve the reliability and acceptability of cable connectors utilized in MWD operations. The apparatus of the present invention is also well suited for well logging operations where two or more lengths of cable must be connected together.